Domain Warm-up for Email Marketing

What is domain warm-up?

Domain warm-up is the process of gradually increasing the volume of emails sent from a new or dormant domain to build a positive reputation with Internet Service Providers (ISPs) and Email Service Providers (ESPs). The goal is to establish trust and avoid being flagged as spam.

Why does domain warm-up exist?

Email providers (like Gmail, Outlook, and Yahoo) monitor new or inactive domains closely to prevent spam and phishing attacks. If a domain suddenly sends a high volume of emails without a history of good sending behavior, it can:

• Trigger spam filters
• Lead to poor email deliverability
• Get blacklisted or marked as suspicious

Domain warm-up ensures that your emails gradually gain trust, allowing you to reach the inbox rather than the spam folder.

Why is domain warm-up necessary?

1. Builds Sender Reputation: ISPs track how recipients engage with your emails (opens, clicks, replies). A slow, steady increase in sending volume helps establish credibility.
2. Avoids Blacklisting: Sudden large-scale email sending from a new domain can get flagged, blocking emails from reaching inboxes.
3. Improves Deliverability: Proper warm-up increases inbox placement rates, ensuring more recipients see your emails.

Best practices for domain warm-up

To successfully warm up a domain and improve email deliverability, follow these key steps:

1. Start with low volume and gradually increase

• Begin with 10-50 emails per day for the first few days.
• Slowly increase by double or 20-30% daily over several weeks.
• Avoid large spikes in volume.

 

2. Target engaged recipients first

• Send emails initially to contacts who are highly likely to open and engage.
• Avoid cold lists; use warm contacts (past customers, subscribers, etc.).
• Focus on personal, non-promotional emails in the beginning.

 

3. Monitor Engagement Metrics

• Track open rates, click-through rates, reply rates, bounce rates, and spam complaints.

 

4. Segment your audience

• Prioritize smaller, engaged segments initially.
• Avoid sending to inactive or unverified contacts early in the warm-up phase.

 

5. Maintain a consistent sending schedule

• Send emails at regular intervals (e.g. weekdays at the same time).
• Avoid erratic or inconsistent sending patterns.

 

6. Gradually expand to promotional emails

• Start with personal or transactional emails before scaling to newsletters or promotions.
• Ensure email content is valuable, engaging, and not overly salesy in the early stages.

 

7. Keep bounce rates low

• Use email verification tools (like AddressCheck) to clean your email list before sending.
• Remove hard bounces and unresponsive contacts.

 

8. Continue building reputation over time

• Domain reputation is ongoing, not a one-time setup.
• Even after warming up, maintain best practices to avoid being flagged in the future.

Typical warm-up timeline

Week Daily Email Volume Target audience

1             10-50                                    Highly engaged contacts

2             100-300.                               Engaged subscribers

3.            500-1000.                             Broader audience, still engaged

4.            2,000-5,000                          Normalized sending to full list

5+.         Scale as needed.                  Full-scale marketing campaigns

Why is domain warm-up necessary even when using reputable mail sending platforms?

Even when using trusted email service providers (ESPs) like Maileon, domain warm-up is still necessary. While we provide reputable IPs, they do not automatically guarantee high deliverability for your domain. Here’s why:

1. ISPs evaluate domain reputation separately from IP reputation

• Mail providers (Gmail, Yahoo, Outlook, etc.) track sender reputation at the domain level, not just at the IP level.
• Even if you send through a shared or dedicated IP with a good reputation, your domain is still new to ISPs.
• Without a warm-up, email providers may classify your domain as suspicious or unverified, resulting in poor deliverability.

 

2. ISPs use „new domain“ suspicion algorithms

• New domains sending large volumes of email are flagged as potential spam or phishing sources.
• To combat abuse, ISPs apply filters and rate limits on emails from new domains.
• A sudden surge in email volume can trigger temporary blocking, spam folder placement, or blacklisting.

 

3. Preventing spam complaints and hard bounces

• If emails from your domain start getting ignored, marked as spam, or bouncing, ISPs associate negative engagement with your domain.
• High spam complaints (above 0.1%) can lead to domain-level blacklisting which makes it hard to recover from public spam lists.
• Gradual domain warm-up helps to ensure that emails land in the inbox, not in the spam folder.

 

4. Dedicated IPs still require domain warm-up

If you’re using a dedicated IP, both the IP and the domain are fresh. This makes warming up even more critical, as ISPs will have no prior trust in either.

 

5. ISPs monitor sending patterns & behavior

ISPs analyse sending consistency, volume, and engagement over time.

• A sudden jump from 0 to 10,000 emails looks unnatural and spam-like.
• A gradual increase over weeks helps to show ISPs that your emails are legitimate.
• If your email campaigns are inconsistent (e.g., sending 50,000 emails one day and none the next), it negatively affects reputation.